Past and Future Solar Activity from Cosmogenic Radionuclides

Abstract

The sunspot record since 1610 shows cycles of magnetic activity with an irregular distribution of amplitudes and with a period around 11 years. They are modulated on longer timescales and were interrupted by the Maunder minimum in the 17th century. During the past several cycles the average solar activity was very high. This raises the question whether the present grand maximum is likely to terminate soon or even to be followed by another (Maunder- like) grand minimum. Cosmogenic radionuclides stored in natural archives such as 10Be in ice cores and 14C in tree rings have proven to be a valuable tool in reconstructing past solar activity and changes in the geomagnetic field intensity over several millennia. At present, this is the only method to extend back the record of solar activity beyond the instrumental period. The main properties of solar activity will be discussed for the past 10,000 years. A detailed statistical analysis of this record allows us to derive the life expectancy of the present grand maximum, which will come soon to an end. By using the same approach applied to the intervals between grand minima, we expect a grand minimum in solar activity to occur within the next 100 years.